Permeability enhancement method for coalbed methane wells by using electric pulse detonation fracturing technology

Abstract

A permeability enhancement method for coalbed methane wells by using electric pulse detonation fracturing technology is applicable to exploitation of coalbed methane wells in coal beds with low permeability. Firstly, a positive electrode coalbed methane wellbore and a negative electrode coalbed methane wellbore are constructed from the ground surface to a coal bed. A fixed platform installed with a positive electrode and a high-voltage pulse device are placed, by using a derrick, downwards to a predetermined permeability enhancement portion of the coal bed in the positive electrode coalbed methane wellbore, and another fixed platform installed with a negative electrode is placed, by using a derrick, downwards to a predetermined permeability enhancement portion of the coal bed in the negative electrode coalbed methane wellbore. The coal bed between the positive electrode and the negative electrode is broken down by using a high voltage, and coalbed methane extraction is carried out in the positive electrode coalbed methane wellbore and the negative electrode coalbed methane wellbore. A large amount of energy produced by high-voltage electric pulse directly acts on the coal reservoir to form a plasma channel in the coal bed between the positive electrode and the negative electrode. The large amount of energy instantly passes through the plasma channel, and the produced high-temperature thermal expansion force and shock waves act on the coal bed, such that the number of cracks in the coal bed is effectively increased and a favorable condition is created for flowing of coalbed methane.

Claims

1. A permeability enhancement method for coalbed methane wells by using electric pulse detonation fracturing technology, comprising the following steps: a. constructing a positive electrode coalbed methane wellbore (2) and a negative electrode coalbed methane well bore (3) from the ground surface to a coal bed (1); placing, by using a derrick (11), a fixed platform (4) installed with a positive electrode (5) and a high-voltage pulse device (7) arranged on the fixed platform (4) downwards to a predetermined permeability enhancement portion of the coal bed (1) in the positive electrode coal bed methane well bore (2), and placing, by using a derrick (11), another fixed platform (4) installed with a negative electrode (6) downwards to a predetermined permeability enhancement portion of the coal bed (1) in the negative electrode coalbed methane wellbore (3), the negative electrode (6) being connected to the high-voltage pulse device (7) through a cable (12), wherein the high-voltage pulse device (7) has a discharge frequency of 5 to 30 Hz and a voltage range of 500 to 9000 KV; b. adjusting, by using a console (8), the fixed platforms (4) in the positive electrode coalbed methane wellbore (2) and the negative electrode coalbed methane wellbore (3), such that upper portions of the fixed platforms (4) are in close contact with wellbore walls, the positive electrode (5) and the negative electrode (6) on the two fixed platforms (4) are then in close contact with the wellbore walls respectively, and the positive electrode (5) and the negative electrode (6) are arranged face to face on the same level; c. turning on a pulse switch (9) to charge the high-voltage pulse device (7) through a cable (10), wherein upon reaching a set discharge voltage, the high-voltage pulse device (7) discharges electricity to the coal bed between the positive electrode (5) and the negative electrode (6) through the positive electrode (5); and turning off the pulse switch (9) after 10 to 100 times of discharge; d. moving the fixed platform (4) installed with the positive electrode (5) and the high-voltage pulse device (7) out of the positive electrode coalbed methane wellbore (2), moving the other fixed platform (4) installed with the negative electrode (6) out of the negative electrode coal bed methane wellbore (3), and starting coal bed methane extraction.

2. The permeability enhancement method for coalbed methane wells by using electric pulse detonation fracturing technology according to claim 1, wherein a distance between the positive electrode coalbed methane wellbore (2) and the negative electrode coalbed methane wellbore (3) is 150 to 1200 m.

3. The permeability enhancement method for coalbed methane wells by using electric pulse detonation fracturing technology according to claim 1, wherein the high-voltage pulse device (7) comprises a capacitor (13) and a pulse trigger (14) connected to the capacitor (13).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a permeability enhancement system for coalbed methane wells by using electric pulse detonation fracturing technology according to the present invention; and

(2) FIG. 2 is a structural diagram of a high-voltage electric pulse device.

(3) In the drawing: 1: coal bed, 2: positive electrode coalbed methane wellbore, 3: negative electrode coalbed methane wellbore, 4: fixed platform, 5: positive electrode, 6: negative electrode, 7: high-voltage pulse device, 8: console, 9: high-voltage electric pulse switch, 10: cable, 11: derrick, 12: cable, 13: capacitor, 14: pulse trigger.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) An embodiment of the present invention is further described below with reference to the accompanying drawings.

(5) As shown in FIG. 1 and FIG. 2, a permeability enhancement method for coalbed methane wells by using electric pulse detonation fracturing technology according to the present invention includes the following specific steps:

(6) (1) constructing a positive electrode coalbed methane wellbore 2 and a negative electrode coalbed methane wellbore 3 from the ground surface to a coal bed 1, a distance between the positive electrode coalbed methane wellbore 2 and the negative electrode coalbed methane wellbore 3 being 150 to 1200 m; placing, by using a derrick 11, a fixed platform 4 installed with a positive electrode 5 and a high-voltage pulse device 7 arranged on the fixed platform 4 downwards to a predetermined permeability enhancement portion of the coal bed 1 in the positive electrode coalbed methane wellbore 2, the high-voltage pulse device 7 including a capacitor 13 and a pulse generator 14 connected to the capacitor 13; and placing, by using a derrick 11, another fixed platform 4 installed with a negative electrode 6 downwards to a predetermined permeability enhancement portion of the coal bed 1 in the negative electrode coalbed methane wellbore 3, the negative electrode 6 being connected to the capacitor 13 of the high-voltage pulse device 7 in the positive electrode coalbed methane wellbore 2 through a cable 12;

(7) (2) adjusting, by using a console 8, the fixed platforms 4 in the positive electrode coalbed methane wellbore 2 and the negative electrode coalbed methane wellbore 3, such that upper portions of the fixed platforms 4 are in close contact with wellbore walls, the positive electrode 5 on the fixed platform 4 in the positive electrode coalbed methane wellbore 2 and the negative electrode 6 on the fixed platform 4 in the negative electrode coalbed methane wellbore 3 are then in close contact with the wellbore walls respectively, and the positive electrode 5 and the negative electrode 6 are arranged face to face on the same level;

(8) (3) turning on a high-voltage electric pulse switch 9 to charge the high-voltage pulse device 7 through a cable 10, where upon reaching a set discharge voltage, the high-voltage pulse device 7 discharges electricity to the coal bed between the positive electrode 5 and the negative electrode 6 through the positive electrode 5; and turning off the high-voltage electric pulse switch 9 after 10 to 100 times of discharge, where the high-voltage pulse device 7 has a discharge frequency of 5 to 30 Hz and a voltage range of 500 to 9000 KV; for example, the high-voltage electric pulse switch 9 is turned off after discharge is carried out on the coal bed between the positive electrode 5 and the negative electrode 6 at a frequency of 5 Hz for 15 times; and

(9) (4) moving the fixed platform 4 installed with the positive electrode 5 and the high-voltage pulse device 7 out of the positive electrode coalbed methane wellbore 2, moving the other fixed platform 4 installed with the negative electrode 6 out of the negative electrode coalbed methane wellbore 3, and starting coalbed methane extraction in the positive electrode coalbed methane wellbore 2 and the negative electrode coalbed methane wellbore 3 according to conventional techniques.